Method of fabrication of an array of graded refractive index microlenses integrated in a image sensor

Abstract

Methods and devices that incorporate microlens arrays are disclosed. An image sensor includes a pixel layer and a dielectric layer. The pixel layer has a photodetector portion configured to convert light absorbed by the pixel layer into an electrical signal. The dielectric layer is formed on a surface of the pixel layer. The dielectric layer has a refractive index that varies along a length of the dielectric layer. A method for fabricating an image sensor includes forming an array of microlenses on a surface of the dielectric layer, emitting ions through the array of microlenses to implant the ions in the dielectric layer, and removing the array of microlenses from the surface of the dielectric layer.

What is claimed: 
     
       1. An image sensor comprising: a pixel layer comprising a photodetector portion, the photodetector portion configured to convert light absorbed by the pixel layer into an electrical signal; and a dielectric layer formed on a surface of the pixel layer, the dielectric layer having a refractive index that varies along a length of the dielectric layer, wherein the length is parallel to the surface of the pixel layer, wherein the refractive index of the dielectric layer comprises relative maximum values at areas centered above respective photodetector portions of the pixel layer, wherein the dielectric layer comprises a base material and includes regions of ions implanted in the base material, and wherein the implanted ion regions are aligned with the respective photodetector portions. 
     
     
       2. The image sensor of  claim 1 , wherein the implanted ion regions generate the variance in the refractive index of the dielectric layer. 
     
     
       3. The image sensor of  claim 2 , wherein
 a refractive index of the implanted ion regions is greater than a refractive index of the base material and wherein the implanted ion regions are centered above respective photodetector portions of the pixel layer. 
 
     
     
       4. The image sensor of  claim 2 , wherein
 the base material comprises silicon nitride, and the implanted ions comprise argon. 
 
     
     
       5. The image sensor of  claim 1 , wherein
 the dielectric layer is formed on a front surface of the pixel layer and the image sensor is configured to receive light through the front surface of the pixel layer. 
 
     
     
       6. The image sensor of  claim 1 , wherein the dielectric layer is formed on a back surface of the pixel layer relative and the image sensor is configured to receive light through the back surface of the pixel layer. 
     
     
       7. An image sensor comprising: a pixel layer comprising a photodetector portion, the photodetector portion configured to convert light absorbed by the pixel layer into an electrical signal; and a dielectric layer formed on a surface of the pixel layer, the dielectric layer having a refractive index that varies along a length of the dielectric layer, wherein the length is parallel to the surface of the pixel layer, wherein the refractive index of the dielectric layer comprises relative maximum values at areas centered above respective photodetector portions of the pixel layer, wherein the dielectric layer comprises a base material and includes regions of ions implanted in the base material, wherein the implanted ion regions generate the variance in the refractive index of the dielectric layer, wherein a refractive index of the implanted ion regions is less than a refractive index of the base material, and wherein the implanted ion regions are centered at the boundaries of respective photodetector portions of the pixel layer.